1. Field of the Invention
The present invention relates to an apparatus for polishing objects such as semiconductor wafers, hard disks, glass substrates, liquid crystal display panels, and so on.
2. Description of the Related Art
A conventional chemical mechanical polishing (CMP) apparatus used in fabrication of, for example, semiconductor integrated circuit devices, is based on holding the semiconductor wafer in a rotating top ring and pressing the wafer against a polishing cloth mounted on a rotating turntable while supplying a polishing solution, including abrading particles to the polishing cloth. Hence, polishing is carried out mechanically by the abrading particles floating freely in the polishing solution, and chemically by a chemical solution at the pressing and sliding interface between the polishing cloth and the semiconductor wafer. However, such a CMP apparatus presents a problem in that, depending on the type of surface patterns and differences in the height of fine structures formed on the surface of the wafer, it was not possible to obtain a precisely polished flat and mirror surface on the wafer.
Therefore, in place of the CMP process, another polishing technology has been developed, based on a grinding member to produce a relative pressing and sliding motion against the wafer, in which abrading particles are bound in the grinding member and generated freely from the grinding member while water or a chemical solution is supplied at the sliding interface between the grinding member and the wafer. The polishing apparatus of the grinding member type includes variations using such as a ring-type grinding wheel attached on a supporting member or a cup-type grinding wheel having ring- shaped pellet attached on a supporting member. These grinding wheels include abrading particles bound therein.
FIG. 1 shows a cross sectional view of a conventional cup-type polishing apparatus using a grinding wheel. A wafer 100 is placed on the top surface of a disk-shaped wafer holder 80. A cup-type grinding wheel 90 comprises of a grinding wheel holder 93 and a ring-shaped grinding wheel 91, which is disposed above the wafer 100. The grinding wheel 91 is pressed and slided against the wafer 100. The wafer holder 80 and the wafer 100 are rotated in the direction of the arrow H while the grinding wheel 91 is rotated in the direction of the arrow J. Also, the grinding wheel 91 moves linearly in the radial direction of the wafer 100 (indicated by the arrows K). Thus, the entire surface of the wafer 100 is uniformly polished by the grinding wheel 91.
In this apparatus, the wafer holder 80 is surrounded with a table surface 95 so that even if the rotational axis m of the grinding wheel 90moves away from the outer periphery of the wafer 100, tilting of the grinding wheel 90 is prevented by supporting the grinding wheel 91 on the table surface 95.
This apparatus presents the following problems.
(1) In this design, it is difficult to adjust the surface levels between the wafer 100 and the table surface 95 so as to keep the same level therebetween, and basically, it is virtually impossible to attain a completely level surface.
(2) Polishing speed of the grinder 90 is rather slow, and the productivity is generally low.
(3) It is necessary to dress the grinding surface of the grinding wheel 91 after a given usage, to refurbish the polishing quality of the grinding wheel 91, using a separate dressing tool. However, when a grinding wheel is being dressed, the wafer 100 cannot be polished. Thus, not only the productivity of polishing is lowered, but additionally, because a space must be allocated for the dressing tool, it becomes difficult to design a compact polishing apparatus using a cup-type grinding wheel.
It is an object of the present invention to provide a polishing apparatus having a grinding member of a compact design that can provide high efficiency for both polishing and dressing operations, and prevents tilting of the grinding member even if the rotation axis thereof is moved away from the outer periphery of the object being polished.
According to the present invention, there is provided a polishing apparatus for polishing an object using a grinding member, comprising an object holder for holding an object to be polished such that a surface to be polished is facing upward, and a dresser disk holder for holding a dresser disk for dressing the grinding member such that a dressing surface of the dresser disk is facing upward. The surface to be polished and the dressing surface are arranged so as to be coplanar. While the grinding member is polishing the object, the grinding member is being dressed by the dresser disk.
The grinding member has an abrasive surface which is facing downward, and the abrasive surface is disposed so as to straddle the surface of the object to be polished and the dressing surface of the dresser disk. The polishing and dressing occur as a result of the grinding member being pressed against and slid relative to the object and the dresser disk.
Accordingly, the polishing apparatus of the present invention provides the following advantages compared with conventional polishing apparatus having a grinding member.
Even when the center of rotation of the grinding member moves away from the outer periphery of the polishing object during a polishing operation, there is no danger of tilting the grinding member because the grinding member is supported also by the dresser disk. This arrangement eliminates the need for a separate table to prevent tilting, and provides an additional benefit in that dressing of the abrasive surface of the grinding member can be performed concurrently with polishing of the surface of the object. Therefore, there is no need to provide a separate dressing step to dress the abrasive surface of the grinding member, thereby increasing the polishing efficiency and providing a compact apparatus.
According to the present invention, a plural of object holders and a plural of dresser disk holders may be disposed for polishing a plurality of objects while the grinding member is being dressed by the plurality of dresser disks.
Accordingly, one grinding member can process a plurality of objects while being processed by a plurality of dresser disks, so that the polishing and dressing productivity is increased and the overall efficiency of the polishing operation is improved.
According to the present invention, a grinding member monitoring device may be provided to check conditions of a dressed abrasive surface of the grinding member, and a control device may be provided to control dressing conditions according to output signals from the grinding member monitoring device.
Accordingly, dressing conditions can be optimized by providing a grinding member monitoring device and a dressing control device.
According to the present invention, a weight limiting device may be provided so as to control a pressure exerted on the surface to be polished by the grinding member.
Accordingly, the polishing load can be decreased to a level, which is lower than the weight of the grinding member by providing a suspending device, which also facilitates vertical movements of a main pressing device to enable fine adjustment in pressure control.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, which illustrate a preferred embodiment of the present invention by way of example.